Carbon Fiber Reinforced Polymer (CFRP) composites exhibit exceptional specific stiffness and strength properties. However, their use in structural applications is often constrained with high safety margins out of concern for their brittle and sudden failures. This study proposes manipulating the tensile failure mechanism by utilizing a discontinuous overlapped architecture, which has been demonstrated in the literature to non-linearize the tensile stress-strain response of CFRP laminates. Continuous Carbon fiber 3D-printing provides freedom in building complex morphologies and adjusting the resin content, enabling intricate discontinuous patterns for further tuning the stress-strain response. This study characterizes the constituents and tensile properties of 3D-printed continuous UD laminates. Then, an investigation is conducted on the mechanical tensile response of a 3D-printed discontinuous laminates design and the effect of discontinuity pattern length, and post-processing.

This research is focused on investigating the effect of carbon nanotubes on macroscale composite laminate properties, such as, interlaminar shear strength, interlaminar fracture toughness and electrical conductivity along with studying the micro and nano-scale interactions of carbon nanotubes with epoxy matrix via thermomechanical and electrical characterization of nanocomposites. First an introduction to the typical advanced composite laminates and multifunctional nanocomposites is provided followed by a literature review and a summary of recent status on the processing and the characterization work on nanocomposites and composite laminates. Experimental approach is presented for the development of processing techniques and appropriate characterization methods for carbon nanotubes reinforced epoxy resin based multi-functional nanocomposites and carbon fiber reinforced polymer composite laminates modified with carbon nanotubes. The proposed work section is divided into three sub-sections to describe the processing and the characterization of carbon nanotube reinforced epoxy matrix nanocomposites, woven-carbon fabric epoxy matrix composite laminates modified with selective placement of nanotubes and unidirectional carbon fiber epoxy matrix composite laminates modified with carbon nanotubes. Efforts are focused on comparing the effects of functionalized and unfunctionalized carbon nanotubes on the advanced composite laminates. Covalently functionalized carbon nanotubes are used for improved dispersion and fiber-matrix bonding characteristics and compared with unfunctionalized or pristine carbon nanotubes. The processing of woven carbon fabric reinforced epoxy matrix composite laminates is performed using a vacuum assisted resin transfer molding process with selective placement of carbon nanotubes using a spraying method. The uni-directional carbon fiber epoxy matrix pre-preg composites are processed using a hot press technique along with the spraying method for placement of nanotubes. These macroscale laminates are tested using short beam shear and double cantilever beam experiments for investigating the effect of nanotubes on the interlaminar shear stress and the interlaminar fracture toughness. Fractography is performed using optical microscopy and scanning electron microscopy to investigate the structure-property relationship. The micro and nano-scale interactions of carbon nanotubes and epoxy matrix are studied through the processing of unfunctionalized and functionalized single wall carbon nanotube reinforced epoxy matrix nanocomposites. The multifunctional nature of such nanocomposites is investigated through thermo-mechanical and electrical characterizations.

Further crosslinking of the fluorinated polyimide was examined to separate the cure reactions from degradation and to determine the optimum post curing conditions. Glass transition/melting temperatures were ascertained using DSC, while weight loss during curing and Td were determined using TGA. Furthermore, the mechanical properties were measured using an Instron to relate to the thermal properties to find the optimum curing conditions. The polyimide resin exhibited the best post-curing conditions for further crosslinking for 8 hours at 410 degress C based on Tg, thermal stability, and mechanical properties. Blister temperatures, resulting from rapid heating, were obtained by monitoring changes in transverse thickness expansion using two different techniques. Both techniques employed showed similar blister temperatures in relation to the amount of absorbed moisture, regardless of sample size. The polyimide resin exhibited blister temperatures ranging from 225 - 362 degrees C, with 1.7 - 3.0 wt% absorbed moisture, and the polyimide composite had blister temperatures from 246 - 294 degrees C with 0.5 - 1.5 wt% moisture. Weight loss of the fluorinated polyimide and its corresponding polyimide carbon fiber composite under elevated temperature was examined. Weight loss as a function of exposure temperature and time was measured using TGA and by pre- and post-weighing of specimens treated in an oven. Both techniques showed similar weight loss trends as a function of time and temperature, but TGA showed much greater weight loss due to greater surface area to volume (i.e., small sample size). The neat polyimide resin and carbon fiber composite exhibited negligible weight loss at temperatures below 430 degrees C for exposure times up to 20 minutes. Transition-metal carbides were initially synthesized by carbothermal reduction of transition-metal halides and polymer precursor mixtures, at temperatures that range from 900 to 1500 degrees C in an argon atmosphere. TaC was synthesized from TaBr5, as a model carbide for this process. Significant (> 40 vol%) amounts of TaC were formed at reaction temperatures as low as 900 degrees C for one hour, with greater times and temperatures leading to > 90 vol% yield. Universality of method was also proven by using other various transition-metal halide salts (NbBr5, WCl4, and WCl6) with the polyimide.

[pt] No Brasil, o dimensionamento de estruturas de concreto armado segue as recomendações da norma brasileira NBR 6118-2003. A norma brasileira, usa a metodologia de dimensionamento semi-probabilístico que não quantifica a probabilidade de falha de um elemento estrutural. A análise de confiabilidade de estruturas é uma ferramenta que possibilita o cálculo da probabilidade de falha associada a um estado limite e também um dimensionamento para uma determinada probabilidade de falha denominada probabilidade de falha alvo. Este trabalho tem como objetivo desenvolver uma metodologia que possibilite o dimensionamento baseado em confiabilidade de seções de vigas de concreto armado sem e com reforço com compósitos de fibras de carbono. Na análise de confiabilidade desenvolvida foram consideradas como variáveis aleatórias o carregamento, as resistências do aço e do concreto, e a resistência à tração dos compósitos de fibras de carbono com propriedades estatísticas determinadas com base nos resultados dos ensaios realizados no laboratório de Estruturas e Materiais do Departamento de Engenharia Civil da PUC-Rio (LEM-DEC). Exemplos de dimensionamento de seções de vigas de concreto armado submetidas à força cortante e à flexão foram realizados inicialmente por métodos semi-probabilísticos e depois utilizando a metodologia proposta baseada em confiabilidade. A análise dos resultados mostra a viabilidade de um projeto baseado em confiabilidade usando um índice de probabilidade de falha determinado para cada tipo de projeto aliando economia e segurança. / [en] In Brazil, the design of reinforced concrete structures follows the recommendations of Brazilian standard NBR 6118-2003. The Brazilian standard uses the methodology of semi-probabilistic design that does not quantify the probability of failure of a structural element. The reliability analysis of structures is a tool that allows the calculation of probability of failure associated with a limit state and also the design for a given probability of failure. This work aims to develop a methodology that enables the Reliability-based-design of concrete beams sections with and without strengthening with carbon fiber composites. In the reliability analysis were considered as random variables the loads, the compression concrete strenght, yield strenght, and tensile strength of carbon fiber composites with certain statistical properties based on the results of tests performed in the Structures and Materials laboratory at PUC-Rio (LEM-DEC). Examples of reinforced concrete beams strengthened with CFC were performed initially by semi-probabilistic methods and then using the proposed methodology based on reliability. The analysis shows the feasibility of a Reliability-baseddesign using a reliability index of failure probability determined for each type of project combining economy and safety.

Indiana University-Purdue University Indianapolis (IUPUI) / This study proposes and evaluates a multi-functional carbon fiber reinforced composite with embedded Lithium-ion battery for its structural integrity concept. The comparison of versatile composite structures manufactured conventionally, air-sprayed and electrospun multi walled carbon nano tubes in order to discover a better packaging method for incorporating lithium-ion batteries at its core is determined. In the electrospinning process recognized globally as a flexible and cost-effective method for generating continuous Nano filaments. It was incorporated exactly on the prepreg surface to obtain effective inter-facial bonding and adhesion between the layers. The mechanical and physical properties of carbon fiber reinforced polymers (CFRP) with electrospun multi walled carbon nano tubes (CNTs) have evidenced to possess higher mechanical strength incorporated between the layers of the composite prepreg than the traditional CFRP prepreg composite, At the same time the air sprayed CFRP with CNTs offers mechanical strength more than the traditional CFRP prepreg but lesser than the electrospun. This can be a design consideration from the economic feasibility viewpoint. They also contribute to efficient load transfer and structural load bearing implementation without compromising the chemistry of battery. The design validation, manufacture methods, and experimental characterization (mechano-electrical) of Multi-functional energy storage composites (MESCs) are examined. Experimental results on the electrochemical characterization reveal that the MESCs show comparable performance to the standard lithium-ion pouch cells without any external packaging and not under any loading requirements. The mechanical performance of the MESC cells especially electrospun CFRP is evaluated from three-point bending tests with the results demonstrating significant mechanical strength and stiffness compared to traditional pouch cells and conventional, air-sprayed CFRP and at lowered packaging weight and thickness. This mechanical robustness of the MESCs enable them to be manufactured as energy-storage devices for electric vehicles.

Hybrid carbon fiber reinforced composites are a new breed of materials that are currently being explored and characterized for next generation aerospace applications. Through the introduction of secondary reinforcements, such as alumina nanoparticles, hybrid properties including improved mechanical properties and stress sensing capabilities can be achieved. In order to maximize these properties, it is necessary to achieve a homogeneous dispersion of particulate filler. Utilizing the photoluminescent properties of alumina, it is possible to compare local levels of particle concentration through emission intensities as a way to determine the effectiveness of the tested manufacturing parameters in increasing material homogeneity. Parameters of these photoluminescence emissions have been established to be stress dependent, which allows for in situ residual stress measurements. It is shown here that the application of silane coupling agents as particle surface treatments improves particle dispersion when compared to untreated samples. Reactive silane coupling agent (RSCA) treatments were found to provide for greater dispersion improvements when compared to non-reactive silane coupling agents (NRSCA). Higher resolution investigations into these samples found that treatment with a reactive coupling agent altered the stress state of particles concentrated around the fiber from a tensile stress state to a compressive stress state. This is proposed to result from bonding of the reactive groups on the coupling agent to the organic groups on the carbon fibers which adjusts the stress state of the particle. Future mechanical tests will verify the effects of the particle surface functionalization treatments on mechanical properties of the composites.

No description available.

A lightweight carbon fiber reinforced polymer (CFRP) sandwich panel has been developed for floor use in commercial office building construction. CFRP laminate skins were combined with low-density rigid polyurethane foam to create a composite sandwich panel suitable for floor use. The CFRP sandwich panel was optimized to withstand code prescribed office-building live loads using a 3D finite element computer program called SolidWorks. The thickness of the polyurethane foam was optimized to meet both strength and serviceability requirements for gravity loading. Deflection ultimately was the controlling factor in the design, as the stresses in the composite materials remained relatively low. The CFRP sandwich panel was then subjected to combined gravity and lateral loading, which included seismic loads from a fictitious 5-story office building located in a region of high seismic risk. The results showed that CFRP sandwich panels are a viable option for use with floors, possessing sufficient strength and stiffness for meeting code prescribed design loads, while providing significant benefits over traditional construction materials.

[pt] Este trabalho experimental tem como objetivo estudar a ductilidade de vigas retangulares de concreto armado reforçadas à flexão utilizando compósitos com tecido de fibras de carbono. No estudo realizado são apresentados os conceitos clássicos de ductilidade e é proposta uma nova sistemática para obtenção do índice de ductilidade, baseada nas considerações da energia elástica e da energia inelástica. A ductilidade é determinada por meio de um índice energético, que se caracteriza como uma forma mais eficiente para a determinação e análise da ductilidade em elementos estruturais. O programa experimental consistiu no ensaio de sete vigas bi-apoiadas, sendo uma viga de referência e as demais reforçadas à flexão com tecido de fibras de carbono. Todas as vigas possuem as mesmas características mecânicas e geométricas e foram dimensionadas de modo a garantir a ruptura por flexão. A viga de referência, a primeira ensaiada, não foi reforçada e serviu para comparações de incremento de rigidez e resistência após a aplicação do reforço. As vigas reforçadas foram divididas em dois grupos. O grupo A é constituído de duas vigas, reforçadas inicialmente com uma e duas camadas de tecido de fibra de carbono. O grupo B é constituído por quatro vigas que foram reforçadas após um carregamento inicial. Neste grupo, duas vigas foram reforçadas com uma camada de tecido de fibra de carbono e as outras duas foram reforçadas com duas camadas de tecido de fibras de carbono, correspondendo à mesma área total de reforço das anteriores. Todas as vigas foram concretadas, instrumentadas e ensaiadas no Laboratório de Estruturas e Materiais da PUC-Rio. Os ensaios das vigas do grupo B foram realizados com as vigas pré-ensaiadas, reforçadas sob deformação constante e em seguida levadas à ruptura. A deformação foi mantida constante durante a aplicação e o período de cura do reforço. Os resultados obtidos em termos de carga, flecha, momento, curvatura, ductilidade energética e rotação plástica foram analisados. Os estudos realizados mostraram que o reforço com compósitos de fibras de carbono é uma técnica eficaz, que as vigas apresentam ductilidade adequada e que os índices energéticos propostos são adequados para este tipo de estudo. / [en] The objective of this experimental work is to study the ductility of reinforced concrete beams strengthened in flexure using externally bonded carbon fiber fabric composites. This study presents the classic concepts of ductility and proposes a new systematic to obtain the ductility index, which is based on the considerations of elastic and inelastic energy. The ductility was determined by an energetic index, which has seen to be a more efficient method to establish and analyze the ductility of structural elements. The experimental program consisted of seven beams tests. One was used as a control beam without external reinforcement and the others were strengthened with carbon fibers in order to resist flexural load. All the beams had the same mechanical and geometrical characteristics and were designed to fail in flexure. The control beam was not strengthened and its purpose was to compare the stiffness increase and resistance after the strength. The strengthened beams were divided in two groups. Group A was constituted by two beams, initially strengthened by one and two layers of carbon fiber fabric. Group B was formed by four beams which were strengthened after the application of an initial load. In this group, two beams were strengthened by one layer of carbon fiber fabric and the other two were strengthened by two layers, which corresponded to the same area of the others. All the beams were cast, instrumented and tested in the Structural and Materials Laboratory at PUC-Rio. Group B tests were performed with the pretested beams strengthened under constant strain, and then loaded up to rupture. The strain was kept constant during the application and cure of the external reinforcement. The results obtained in terms of load, deflection, resistant moment, curvature, energetic ductility indexes and plastic rotation were analyzed. The study showed that the reinforcement using carbon fiber fabric composites is an efficient technique, the beams presented adequate ductility and the proposed energetic ductility indexes are consistent formulae for this kind of study.

[pt] Este trabalho de natureza experimental tem como objetivo estudar o comportamento de vigas de concreto submetidas à torção e reforçadas externamente com compósitos de fibras de carbono (CFC). Treze vigas de concreto com 2,0 m de comprimento e seção transversal de 30 cm х 60 cm foram testadas no Laboratório de Estruturas e Materiais do Departamento de Engenharia Civil (LEM/DEC) da Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio). As vigas foram divididas em quatro séries, sendo uma de referência, composta por quatro vigas sem reforço externo, e outras três séries constituídas por três vigas que foram reforçadas externamente com taxas crescentes de estribos de CFC. Com o propósito de estudar a contribuição do concreto e do reforço de CFC na resistência à torção de vigas, a armadura interna só foi colocada na região de aplicação de cargas e nos apoios para evitar a ruptura local e possibilitar o estudo da região central sem a parcela resistente devida à armadura interna de aço. Os resultados dos ensaios mostraram que as vigas reforçadas apresentaram aumento de carga de fissuração entre 16 por cento e 56 por cento e um acréscimo de resistência à ruptura entre 19 por cento e 47 por cento quando comparadas às vigas de referência. A rigidez das vigas na ruptura aumentou proporcionalmente ao crescimento da taxa de reforço como observado em outros ensaios encontrados na literatura. / [en] This research is an experimental study of torsion strengthening of concrete beams with carbon fibers composites. Thirteen concrete beams with 2.0 long and 30 x 60 cm cross section were tested in the Structures and Materials Laboratory of the Civil Engineering Department (LEM/DEC) of Pontifical Catholic University of Rio de Janeiro (PUC-Rio). The beams were divided in four series, the first one was called the reference series and consisted of four beams without external strengthening and each of the other three series was composed of three beams strengthened with increasing rates of external carbon fibers composites stirrups. In oder to allow the study of the central region without the contribution of the steel reinforcement, the internal steel reinforcement was placed only at points of loads application and supports to prevent the local rupture. The tests results showed that the strengthened beams had an increase of the cracking load between 16 per cent and 56 per cent, and an increase of the rupture load between 19 per cent and 47 per cent when compared to the reference beams. The ultimate resistance of the beams increased proportionally to the rate of external carbon fibers composites strengthening, as was observed by other researchers.